This invention relates to power down circuitry for use in battery operated electronic devices, and more particularly the invention relates to power down circuitry in such devices which can be distributed to and incorporated in integrated circuits of the devices.
Power consumption and the conservation of energy is a particular concern in battery operated devices such as portable lap top computers, portable phones, battery powered field test equipment, and the like. Traditional power conservation relies on switching power on and off to major subassemblies, or to sections of electrical circuitry on a printed circuit board. This can require bulky, high current switching devices and introduce unwanted design constraints.
Integrated circuit technology advances have resulted in a dramatic increase in analog integrated circuit density. Early analog circuits included many discrete components that were encapsulated into a module. However, the discrete components, such as an operational amplifier, can now be formed as an integral part of an integrated circuit. Heretofore, some integrated circuits such as random access memories (RAMs) have been provided with chip enable pins through which a chip select signal could be applied in controlling power to the chip. However, in many existing analog integrated circuits no provision has been made for select pins in receiving power control signals. Power control in such circuits through use of external power switches, multiplexing digital outputs in ADC circuits, altering the analog output, or stopping a clock in one state have been considered but are not feasible design alternatives.
The present invention is directed to providing analog integrated circuits, such as ADC and DAC circuits which require external reference voltages, with internal circuitry for power control based on the presence or absence of the reference voltage.